The New York-based watchdog charged that the Saudi-led coalition had failed to investigate alleged breaches of the rules of war during the bombing campaign it launched against Shiite rebels in March and called for a UN probe.
It said that 10 children were among the dead in Friday’s strikes in the Red Sea port of Mokha.
Coalition warplanes repeatedly struck two compounds housing the families of workers at the Mokha Steam Power Plant, it added.
“With no evident military target, this attack appears to be a war crime,” said the watchdog’s senior emergencies researcher, Ole Solvang.
HRW called for a UN probe into allegations against all parties to the conflict, including the coalition, loyalists of the exiled government it is seeking to restore, and the rebels and their allies.
“The failure of Saudi Arabia and other coalition members to investigate apparently unlawful air strikes in Yemen demonstrates the need for the United Nations Human Rights Council to create a commission of inquiry,” it said.
The United Nations says the conflict has killed more than 3,640 people, around half of them civilians, since late March.
On Monday, the coalition began a five-day pause in its bombing campaign to allow delivery of desperately needed relief supplies.
But the International Committee of the Red Cross has warned that five days are not enough to cover the needs.